Inorganic substrates such as metal, glass, or metal-deposited surfaces are coated at room temperature or by baking after various chemical conversions or application of primers. Patent Literature 1 suggests a method in which a composition formed from an acid functional aliphatic polyester polyol and polyisocyanate is directly applied to a cold-rolled steel plate or the like, but this method still involves baking at a temperature as high as at least 100° C. for a long period of time. Moreover, Patent Literature 2 discloses a method in which an alkoxysilyl group-containing acrylic polymer or the like is directly applied to an aluminum plate, but this method involves curing at room temperature or baking.
Meanwhile, glass is used in various building components such as windows and sidings, automobiles and railway vehicles due to its excellent optical transparency, dimensional stability in various temperature ranges and gas barrier properties. In recent years, with its advantage of optical transparency, dimensional stability, and rigidity, glass has been widely used in displays of information and communication devices such as liquid crystal displays and plasma displays.
However, glass has a major drawback in that it is fragile with low resistance to impact or that broken glass scatters. This feature is remarkable particularly in human-carried applications such as information and communication devices.
At the same time, a demand for thinner and lighter displays of information and communication devices has been increasing. Accordingly, cover glass and glass sensors also tend to be thinner, making them more fragile during use. In addition to the impact on the human body due to breakage, breakage of such cover glass or glass sensors, which are expensive materials, namely means that the entire terminal device can no longer be used.
In this context, for example, Patent Literature 3 suggests that breakage and scattering of glass can be greatly prevented by attaching a multilayer laminated film including a polyethylene terephthalate layer and a sebacic acid-copolymerized polyethylene terephthalate layer to a glass surface.
Although the method disclosed in Patent Literature 3 is effective in preventing breakage and scattering of glass, since the sebacic acid-copolymerized polyethylene terephthalate layer included in the multilayer laminated film has a low glass-transition temperature, crystallization gradually proceeds and a blushing phenomenon occurs, resulting in higher haze.
Patent Literature 4 suggests a glass protection film that prevents scattering of glass and such a blushing by use of a film having a multilayer structure in which the haze value and the difference in glass-transition temperature of the film are specified. However, it has problems in that, for example, the difference in glass-transition temperature is large and therefore the film may exhibit dimensional discrepancies depending on the use conditions, and that a special laminating device is required to superimpose the films in a multilayer manner.
A method of applying a coating agent to glass to protect the surface or impart functionality to the surface is also suggested. For example, Patent Literature 5 suggests a method in which a composition essentially containing a thermoplastic polyurethane resin, an epoxy resin or melamine added to an aqueous polyurethane is used as a glass coating material.
However, the object of the method disclosed in Patent Literature 5 is to increase resistance of glass to alkaline washing, and the method involves curing at a temperature as high as at least 100° C. for a period as long as at least 10 minutes to form a coating.
Meanwhile, pre-coated metals are used in which coating is preliminarily applied to a metal plate and then formed into a given shape to be used in a final application. Such a pre-coating method has advantages over the post-coating method in which a metal plate is first formed into a complicated shaped article and then coated, such as rationalized coating step, uniform quality, reduced consumption of coating materials, and so forth. Thus, its application can also be expected to increase in the future.
In this application, a galvanized steel plate or an aluminum plate is subjected to phosphating treatment or chromate treatment to apply a chemical conversion coating and a primer such as an epoxy resin primer or a polyester resin primer is preliminarily applied to the plate before a coating composition for pre-coated metals is applied. In this case, baking at a temperature higher than 200° C. is required.
Since coatings formed from pre-coated metal coating materials are formed into a shape according to the application, the coatings of the coating materials are required to maintain sufficient flexibility enough to withstand forming and sufficient adhesion to the metal surfaces. Then, formed products are required to have properties suitable for the final applications, such as, for example, high weather resistance for use in building exterior materials.
The conventional materials that have been used as pre-coated metal coating materials, such as polyester resin, amino alkyd resin, and thermosetting acrylic resin, have problems in that after processed by forming, their coatings often suffer from cracking or peeling from the steel plate. As a technique to prevent such problems, a wax is used as an internal lubricant. Patent Literature 6 discloses a method of producing a pre-coated metal by applying a composition containing a blocked isocyanate compound blocked with ethyleneimine and a polyol resin to a metal plate and thermally curing the composition. Yet, this method is unable to satisfy all the physical properties descried above.
Patent Literature 7 also suggests a heat-curable, pre-coated metal coating material containing a polyol, an aliphatic or alicyclic blocked polyisocyanate, and an anti-thermal yellowing agent for outside applications and others requiring weather resistance. Yet, it is unable to meet weather resistance sufficiently.
Moreover, Patent Literature 8 suggests curing by active energy rays in order to shorten the process such as curing time and to reduce the energy costs associated with baking at high temperatures. However, it involves the preliminary formation of a chemical conversion coating followed by application to a substrate on which a primer has been applied. No conventional active energy ray-curable materials can be applied directly to metal substrates or chemical conversion coatings.
Furthermore, for excellent design and excellent appearance, composite materials of organic and inorganic substrates are increasingly used in substrates or components to be coated. This has created a desire for an active energy ray-curable coating agent that can successfully adhere to both organic and inorganic substrates; however, no existing coating agents satisfy such properties.